Crude oil arriving at a refinery normally contains small amounts of water, solids, inorganic salts, and the like. To be effectively processed in a refining process, the crude oil is normally subjected to a desalting process whereby it is washed with water to remove soluble chloride, sulfate, and other corrosion causing salts. The art of desalting is well known to those skilled in the art of petroleum processing and will not be discussed herein in great detail. After the desalting process, the crude oil now containing a diminished amount of water and inorganic salts is subjected to processing. Normally one of the first processing steps is the distillation of the crude oil to separate it into fractions suitable for sale.
In the distillation of the crude oil high temperatures and pressures can be applied. If corrosion causing acid components are present along with small amounts of water, corrosion of distillation columns, overhead lines, processing lines and the like can take place. Likewise, solids remaining in the oil are generally treated by adding a dispersant to the crude oil. The dispersants serve to prevent the fouling of lines, overheads, and the like with asphaltenes.
Asphaltenes are the heaviest and the most polar components of crude oils. They are generally defined as a solubility class of the polydisperse, high molecular hydrocarbons which are insoluble in nonpolar solvents. Asphaltene particles are believed to exist in the form of colloidal dispersion stabilized by other components of the crude oil. These naturally occurring dispersions can be destabilized by a variety of mechanical and chemical conditions involved in oil production and processing. This can result in asphaltene aggregation, precipitation and eventual deposition of a tarry residue. Once precipitated, asphaltene solids pose a multitude of technological difficulties to crude oil production in that permeability blocking in the reservoir matrix, wells and pipelines. Likewise, plugging, deposition in treating vessels and the narrowing of flow lines can occur in processing. In the refinery processing of heavy crude oils, asphaltenes are known to foul metallic heat transfer surfaces, decreasing heat transfer efficiency.
The use of chemical treatments to inhibit asphaltene precipitation has become very important with the current tendency in the petroleum industry towards the exploration, drilling, production and processing of heavier oils, higher in asphaltene content. In recent years, a significant increase in the use of asphaltene inhibitors/dispersants has resulted. Asphaltene dispersants are known to aid in the production and processing of asphaltene crude oils. Among the references describing asphaltene dispersants are U.S. Pat. Nos. 4,931,164; 4,997,580; 5,112,505; and, U.S. Pat. Nos. 5,01,498; 5,073,248; 5,100,531 and 5,143,594 which disclose the use of a combination of two materials, an alkyl substituted phenol-formaldehyde resin and various hydrophilic-lipophilic vinylic polymers.
Refinery processing of heavier crude oils is greatly enhanced by the use of asphaltene dispersants which are used to prevent deposition throughout the entire crude oil handling process. While functioning satisfactorily in crude oil handling units not treated by alkali to control corrosion, decreases in performance are typically observed for known asphaltene dispersants when refinery systems are treated with caustic to reduce corrosion.
When used to control corrosion in crude units, only relatively small amounts of sodium hydroxide (caustic) are added, normally about 2 pounds per 1000 barrels of crude oil, or a level of about 20 parts per million of NaOH per million parts of crude oil. In addition, after proper desalter treatment, there is generally only 0.2% by weight water left in the crude.
This invention is related to a class of asphaltene dispersants that do not lose their activity when used in crude oil treated with caustic. The novel asphaltene dispersants of this invention are alkylphenol-formaldehyde and alkylphenol-polyethylenepolyamine-formaldehyde resins which are economical, commercially available, and do not interfere with other refinery operations.